A typical sieve assembly, such as those found on combines, includes a frame supported for movement over ground and a plurality of laterally-extending slats supported by the frame. Adjacent slats define openings for material, such as grain, to pass through to be separated from unwanted material, such as stems, cobs, stalks, and straw. Typically, the slats are rotatable by a sliding bar/crank adjusting mechanism to adjust the size of the openings between adjacent slats.